Handbook Of Shaft Alignment Episode 1 Part 8 pps

5.2 DIAL INDICATOR BASICS Since the use of dial indicators will be discussed frequently in this chapter, Figure 5.1 shows the basic operating principle of this versatile measurement tool. It is highly recommended to get familiar with this device since it will be used for a wide variety of tasks in the overall process of machinery installation, troubleshooting, problem solving, and shaft alignment. 5.3 DAMAGED, WORN, OR IMPROPERLY INSTALLED MACHINERY COMPONENT CHECKS Every once in a while, you may have the pleasure of installing brand new rotating machinery. If you are in the construction industry that is primarily what you will be doing. However, in a maintenance organization, you will very likely be working with equipment that has been in service for sometime and invariably it is required to find and correct a problem with the 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 Bottom plunger type Back plunger type Dial indicator basics 0 50 10 40 20 30 + _ 10 40 20 30 −70 −25 +40 +75 Stem mov es outward Needle rotates counter clockwise Stem moves inward Needle moves clockwise 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 FIGURE 5.1 Dial indicator basic operation. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 180 26.9.2006 8:36pm 180 Shaft Alignment Handbook, Third Edition equipment. Chapter 1 discussed the four different maintenance philosophies. The ultimate goal of a quality maintenance group is to achieve proactive or prevention maintenance status. The capacity to detect ensuing problems with machinery, stop the damage before it becomes a financial loss to the company, have the capability to quickly detect the problems with the equipment, and engineer the corrective measures to prevent the malady from occurring again is the ultimate goal. Very few people have been able to attain this level of performance. This chapter discusses many of the tasks that make the difference between run-to-failure mainten- ance and proactive or preventive maintenance. If machinery has been operating for sometime, the bearings that support the rotor may have sustained some damage and it is suggested that some checks should be made to insure that the bearings are in good working order. One of the simplest tests that can be performed is a shaft ‘‘lift check’’ as shown in Figure 5.2 and Figure 5.3. Positioning a dial indicator on top of the shaft as close as to get it to the inboard bearing, it is essential to anchor the indicator to a stationary object with a magnetic base or a clamp. Then lifting the shaft upward enough to detect if any motion occurs, but not with so much force as to permanently deform the shaft, can easily happen by using a hydraulic piston, chain hoist, or overhead crane. If the shaft is supported in rolling element-type bearings as shown in Figure 5.4, the amount of lift on the shaft should be negligible (i.e., 0 to maybe 1 mil). If there is an excess amount of shaft lift with a rolling element bearing, four possible reasons for this is as follows: 1. The inner race of the bearing is loose on the shaft. 2. There is too much clearance between the rolling elements and the inner and outer raceways. 3. The outer race is loose in its housing. 4. A combination of two or more of the items above. Shaft lift check Lift upward on each shaft and note the dial indicator readings Place the indicators on top of the shaft or coupling hub and hold the dial indicators steady FIGURE 5.2 How to perform a shaft lift check. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 181 26.9.2006 8:36pm Preliminary Alignment Checks 181 If the inner race is loose on the shaft, the inner race will begin ‘‘skidding’’ on the shaft, eventually damaging the shaft (if it has not already done so). If this condition exists, the machine’s running is stopped immediately and the bearing is removed to make a thorough inspection of the shaft, bearing, and bearing housing. The shaft and the bearing have to be replaced. If there is too much clearance between the rolling elements and the inner and outer raceways, the rollers will begin skidding on the raceways, eventually damaging the bearing (if it has not already done so). If this condition exists, the machine’s running is stopped immediately and the bearing is removed to make a thorough inspection of the shaft, bearing, and bearing housing. The shaft and the bearing have to be replaced. FIGURE 5.3 Performing a lift check on a pump shaft. Rolling element bearings began to appear in the early 1900' s and are also referred to as antifriction or ball bearings. The bearing consists of an inner race, rolling elements, and an outer race. Sometimes the rolling elements are held in place with a cage assembly. As the shaft turns, a film of lubricant forms between the rolling elements and the raceways. The oil film thickness can range between1 and 3 µm (4 to 12 millionths of an inch) and the oil pressures at the minimum oil film thickness are very high (approximately 40 kpsi). If the oil film breaks down, metal to metal contact between the rolling elements and the raceways can occur causing damage to the bearing. Damage to the rolling elements, raceways, or cage assembly can be detected through vibration analysis. Inner race Outer race Rolling elements FIGURE 5.4 Rolling element bearing design. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 182 26.9.2006 8:36pm 182 Shaft Alignment Handbook, Third Edition If there is too much clearance between the outer race and the housing, the outer raceway will begin skidding on inside the housing and eventually damaging the housing (if it has not already done so). If this condition exists, the machine’s running is stopped immediately and the bearing is removed to make a thorough inspection of the shaft, bearing, and bearing housing. The bearing housing and machine case have to be replaced. There are other types of ‘‘fixes’’ possible for items 1 and 3 (i.e., loose inner or outer race) but they are usually not recommended for long-term satisfactory performance. It may be tempting to use epoxy-based adhesives between the raceway and shaft or raceway and housing but that is not the best corrective measure. Sounds like a good idea until you have to remove the bearing at some later date. It may be tempting to sleeve the shaft or the housing but that is also not the best corrective measure. The ability to make a sleeve to achieve the correct interference fits enables to fix the sleeve correctly in the first place. It is recommended to consult the equipment manufacturer for the correct procedure for installing new bearings and the proper type and amount of lubricant to use for that bearing. If the shaft is supported in sliding-type bearings, the amount of lift on the shaft should be within the acceptable radial bearing clearance range. Figure 5.5 shows the basic operating principle of sliding-type bearings. As noted in Figure 5.5, the ‘‘rule of thumb’’ for radial bearing clearance should be from 3=4 to 2 mils=in. of shaft diameter for oil-lubricated babbit bearings. If the amount of lift is greater than the maximum clearance for that shaft diameter, the bearing should be removed and inspected. With cylindrical sliding-type bearings, another Radial (aka diametral) bearing clearance should range from 3/4 to 2 mils/in. of shaft diameter (e.g., a 4 in. diameter shaft should have a clearance range of 0.003 to 0.008 in.) Measure with Plastigage up to 8 mils and soft solder above 8 mils Radial (aka diametral) bearing clearance These are the oldest bearings known to man dating back thousands of years. As the shaft rotates, a wedge of oil forms between the shaft and the bearing surfaces lifting the shaft upwards. Once the oil wedge is formed, the shaft moves slightly to one side and does not run in the exact center of the bearing. The minimum oil film thickness occurs at a line drawn through the shaft and bearing centerlines called the shaft attitude angle. The minimum oil film thickness can range from 0.3 to 2 mils and acts as a damping medium for small amounts of shaft motion (vibration) The lubricant used in rotating machinery is typically oil but the lubricant could really be any fluid (compressible or incompressible, e.g., water or nitrogen) under varying circumstances or, for environmental reasons.These bearings are also known as : • Hydrodynamic bearings • Plain bearings • Journal bearings • Sleeve bearings • Babbit bearings Babbit (lead−tin alloy) HousingLubricant Shaft Shaft “attitude” angle FIGURE 5.5 Sliding bearing design. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 183 26.9.2006 8:36pm Preliminary Alignment Checks 183 recommended method for checking bearing clearance is given in Figure 5.6. Plastigage or soft solder can be used for the clearance check. In addition to the clearance check, a ‘‘tilt and twist’’ check should be made as shown in Figure 5.7. The tilt and twist checks are performed to determine if the centerline of the bore of the bearing is parallel to the centerline of rotation of the shaft in the up and down (tilt) and side-to-side (twist) direction. An alternative check is a ‘‘blue check’’ where a thin coat of Prussian bluing is applied to the lower half of the bearing. The bearing is then installed into its lower hemisphere, and the shaft is lowered onto the bearing and then lifted to allow the removal of the lower half of the bearing. The bearing is then examined to determine how much of the bluing is transferred to the shaft to insure that there is at least 80% shaft to bearing contact. Figure 5.8 shows a bearing in the process of blue checked. Bearing in mind that blue checking will determine if there is a tilt problem but not necessarily a twist problem. Some bearings are spherically seated in their housing to hopefully compensate for any tilt and twist conditions. Figure 5.9 shows an arrangement for a large steam turbine bearing Sliding bearing clearance checks Radial (aka diametral) bearing clearance should range from 3/4 to 2 mils/in. of shaft diameter (e.g., a 4 in. diameter shaft should have a clearance range of 0.003 to 0.008 in.) Remove the upper bearing half and place some Plastigage or soft solder on the top of the shaft Upper bearing housing Lower bearing half Upper bearing half Bearing pedestal or machine case Radial (aka diametral) bearing clearance Shaft Install the upper bearing half and tighten the bolts to the appropriate value Remove the upper bearing half and measure the width of the Plastigage or thickness of the soft solder FIGURE 5.6 Sliding bearing clearance checks. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 184 26.9.2006 8:36pm 184 Shaft Alignment Handbook, Third Edition Tilt and twist in a sliding bearing Remove the upper bearing half and place some Plastigage or soft solder on the top of the shaft Install the upper bearing half and tighten the bolts to the appropriate value Remove the upper bearing half and measure the width of the Plastigage or thickness of the soft solder at both ends. If the thickness is not the same, a tilt condition exists Bearing is in a tilted position Bearing is in a twisted position Remove the upper bearing half and measure the gaps on both sides of the shaft at the front and back of the bearings with feeler gauges Gap? Gap? Gap? Gap? If all four gaps are not the same amount and equal to half of the total radial bearing clearance, a twist condition exists FIGURE 5.7 Finding a tilt and twist problem in a sliding bearings. FIGURE 5.8 Checking contact on a sliding bearing with bluing. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 185 26.9.2006 8:36pm Preliminary Alignment Checks 185 where the bearing assembly is held in position with three support blocks. Shims can be added or removed from each support block to position the bearing in the vertical and lateral directions and to allow for a small amount of clearance to enable the bearing and pads to pivot in the spherically shaped housing. A shaft supported in sliding-type radial bearings can float axially and therefore requires some device (or force) to maintain its correct axial position. In electric motors supported in sliding-type radial bearings, the electromagnetic force centers the armature in the housing. This is often referred to as magnetic center or ‘‘mag center.’’ To find mag center, it is necessary to disconnect the coupling between the motor and what it is driving, and to start the motor up and run it ‘‘solo.’’ When the motor has attained its normal operating speed, it is advised to scribe a line with a felt tip pen or soap stone onto the rotating shaft (care should be taken while doing this) near the inboard bearing using the seal housing or another stationary object on the motor as a reference point. The motor is de-energized (i.e., shut down) and to stop the armature from rotating. After properly safety tagging the breaker, the armature is rotated by hand and as it is rotating, the armature in the axial direction is pushed or pulled until the scribed line that was made on the shaft aligns with the selected stationary reference. This is where the armature wants to run under normal operating conditions. This will become important later on during the alignment process to get the correct axial position between the shafts. Other rotating machines supported in sliding-type radial bearings do not have an electro- magnetic force to center the shaft like motors do. So a thrust bearing is used. There are three major components to a thrust bearing: 45˚ Shims Lower bearing half Machine housing Shaft Upper bearing half Upper bearing retainer FIGURE 5.9 Spherically seated sliding bearing on adjustable support blocks. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 186 26.9.2006 8:36pm 186 Shaft Alignment Handbook, Third Edition 1. The thrust runner or thrust disk: This is a disk permanently attached to the shaft. 2. An active thrust bearing: This is the bearing that the thrust runner typically seats against while it is operating. A film of lubricant prevents the thrust runner from wearing the thrust bearing out. 3. An inactive thrust bearing: It looks the same as the active thrust bearing and under normal operation the thrust runner never seats against it, since most machinery wants to thrust in one direction only. However, if the shaft wants to move in the opposite direction, this bearing will stop the shaft before it contacts something stationary in the machine. Some of the most catastrophic failures of machinery have occurred due to a thrust-bearing failure or due to improperly installing and setting the correct thrust-bearing clearance. To check this clearance, it is essential to position a dial indicator on the end of the shaft (or coupling hub) and anchor the indicator to a stationary object with a magnetic base or a clamp. The shaft toward the operator is pulled until it seats against one of the thrust bearings and zero the indicator as shown in Figure 5.10. The shaft away from the operator is pushed until it seats against the other thrust bearing as shown in Figure 5.11. This is repeated for two or three times and the amount of indicator travel each time is observed. Typically, the thrust- bearing clearance is somewhere between 15 and 40 mils but it is recommended to consult the equipment manufacturer for the correct thrust-bearing clearance and the procedure to correct it if it is not within the recommended range. Figure 5.12 shows a lower half of a tilt pad-type sliding bearing. Notice that there is some evidence of wear in the pads. With tilt pad-type sliding bearings, a mandrel (a cylindrical bar machined to the same outside diameter as the shaft) is used in concert with a dial indicator for the clearance check. This can be done on a table and the procedure is the same as the shaft lift check except that the mandrel is placed in a vertical position, the assembled bearing is slid FIGURE 5.10 Performing a thrust-bearing clearance check, step 1. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 187 26.9.2006 8:36pm Preliminary Alignment Checks 187 over the mandrel, and a dial indicator is positioned against the bearing and then anchored to the table. The bearing is then moved toward and away from the dial indicator to measure the clearance. The radial bearing clearances mentioned above are not for all types of sliding-type bear- ings. Water-lubricated ‘‘cutlass’’-type bearings have greater clearances. New cutlass bearings typically have clearance between 15 and 20 mils and maximum clearances typically should not exceed 80 mils. With these types of bearings, clearance checks can be made with feeler gauges at four points around the circumference of the bearing. A cutlass bearing with excessive clearance on a dredge drive shaft is shown in Figure 5.13. Figure 5.14 shows the feeler gauge readings on that bearing, indicating an excessive amount of clearance. Notice that there seems to be a twist problem with this bearing. The condition and fit of bearings is extremely FIGURE 5.11 Performing a thrust-bearing clearance check, step 2. FIGURE 5.12 Lower half of a tilt pad-type sliding bearing. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 188 26.9.2006 8:36pm 188 Shaft Alignment Handbook, Third Edition important in rotating machinery and should be one of the first items that should be checked before alignment but there are other components that need to be examined for mechanical integrity. In a large majority of rotating machinery, some type of fluid or gas is present inside the machine case and unless it is sealed properly, the fluid or gas will leak out. The lubricant in the bearings can also leak out if proper sealing is not achieved. Sensory clues are the first sign of trouble with seals. If one can notice the seeping out of oil from the machine case under the shaft or oil on the base plate, it is a sign that leakage is occurring. Air or steam leaks frequently can be audibly detected (sound). Frequently high-pressure leaks can be outside the range of human detection and may require leak detection sensors and FIGURE 5.13 Cutlass-type water bearing with excessive clearance. 0.145Љ 0Љ 0.037Љ 0.098Љ Diesel side Pump side 0.198Љ 0Љ 0.125Љ 0Љ FIGURE 5.14 Measured clearances on above bearing. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 189 26.9.2006 8:36pm Preliminary Alignment Checks 189 [...]... Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 2 01 26.9.2006 8: 36pm 2 01 Preliminary Alignment Checks 6 10 _ 0 + 30 50 40 20 30 30 _ 0 + 20 40 10 20 10 10 30 10 0 _ 0 + 20 6 40 10 50 40 20 20 30 30 40 40 50 Coupling hub bored off center 11 7 2 10 10 10 _ 0 + 20 20 30 30 50 20 30 30 30 40 50 10 30 40 20 _ 0 + 20 10 10 20 40 _ 0 + 50 40 40 40 Bent shaft 2 10 10 _ 0 + 20... vertical drive shaft above a threaded coupling Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 19 8 19 8 26.9.2006 8: 36pm Shaft Alignment Handbook, Third Edition FIGURE 5. 28 Measuring runout on the same drive shaft near the top of the shaft FIGURE 5.29 Measuring runout on a stub shaft Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 19 9 Preliminary... clearance Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 19 2 19 2 26.9.2006 8: 36pm Shaft Alignment Handbook, Third Edition Stuffing box 1. 1 18 Љ 1. 003Љ 1. 046Љ West Pump shaft East 0. 985 Љ FIGURE 5 .17 Stuffing box clearance measured on pump in Figure 5 .16 more commonly used lubricant seals: lip seals and labyrinth seals Lip seals are frequently made of rubber and can easily... length of Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 19 5 26.9.2006 8: 36pm 19 5 Preliminary Alignment Checks Checking shaft and coupling hub “runout” Keep the dial indicator still 01 + 0_ 01 02 02 03 03 04 05 04 Rotate this shaft through 360˚ The dial indicator can be mounted like this also 10 20 _0 + 10 20 10 20 30 30 40 50 40 _0 + 10 20 30 30 40 50 40 10 20 _0 +10 10 ... Final Proof page 2 08 2 08 26.9.2006 8: 36pm Shaft Alignment Handbook, Third Edition Soft foot example 2 10 3 5 10 15 5 0 0 0 10 8 20 5 5 0 10 0 20 4 0 4 0 15 15 0 12 22 12 12 17 27 5 5 10 5 0 0 2 4 2 5 5 5 FIGURE 5.42 Soft foot example probably some warpage occurring across those two bolts but do not do anything yet Leave both bolts loose 5 Continue loosening each of the remaining bolts, holding the... the shaft There were 12 þ mils of runout discovered at the measurement taken in Figure 5.27 and 15 þ mils of runout discovered at the measurement taken in Figure 5. 28 with the ‘‘high spots’’ in the same angular Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 19 6 19 6 26.9.2006 8: 36pm Shaft Alignment Handbook, Third Edition FIGURE 5.23 Measuring runout on a long drive shaft. .. to severe misalignment conditions Figure 5. 21 shows extreme wear on a new elastomeric coupling which had been subjected to 20þ mils=in of misalignment that occurred over a period of just 30 weeks of intermittent operation FIGURE 5.20 Excessively worn gear coupling Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 19 4 19 4 26.9.2006 8: 36pm Shaft Alignment Handbook, Third... centerlines of rotation of each shaft are identified and then placed in a collinear axis Ignoring the possibility of runout and very possible aligning of two bent shafts lead to a huge mistake Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 202 202 5.5 26.9.2006 8: 36pm Shaft Alignment Handbook, Third Edition MACHINE HOUSING TO BASE PLATE INTERFACE PROBLEMS One of the most... discussed in Chapter 11 FIGURE 5. 31 Measuring radial runout on a multi-V sheave Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 200 200 26.9.2006 8: 36pm Shaft Alignment Handbook, Third Edition FIGURE 5.32 Measuring face runout on a multi-V sheave Runout checks are frequently made from the inboard bearing to the end of a shaft At the end of a shaft typically a coupling...Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 19 0 19 0 26.9.2006 8: 36pm Shaft Alignment Handbook, Third Edition equipment to be located The typical range for hearing for humans is from 20 to 20,000 Hz (1 Hz ¼ 1 cycle per second) To contain compressible or incompressible fluids inside a machine case, there are four most commonly used types of shaft seals: labyrinth, . a shaft lift check. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 18 1 26.9.2006 8: 36pm Preliminary Alignment Checks 18 1 If the inner race is loose on the shaft, . box Pump shaft 1. 1 18 Љ 0. 985 Љ 1. 046Љ 1. 003Љ West East FIGURE 5 .17 Stuffing box clearance measured on pump in Figure 5 .16 . FIGURE 5 . 18 Oil seal installed backwards on a motor. Piotrowski / Shaft Alignment. drive shaft near the top of the shaft. FIGURE 5.29 Measuring runout on a stub shaft. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C005 Final Proof page 19 8 26.9.2006 8: 36pm 19 8 Shaft